The development of solid electrolytes for polymer lithium batteries has been a major challenge in the energy storage industry. In present lithium battery technology, organic solvents are customarily used as a means of ionizing the ionic lithium salt and concurrently promoting ion transport through polymeric membranes. However, the interaction between the solvents and the electrodes leads to contamination, which in turn reduces the battery shelf-life. Additionally, the organic solvents are contained in metal containers of various shapes, making such batteries heavy and bulky such that significant space is required for intended applications, for instance, in electric vehicles. Moreover, damaged or leaky battery containers can present a safety risk.
As a result, several major efforts have been directed to fabrication of non-volatile conductive membranes, notably polymer gel based electrolytes. The conventional polymer electrolyte utilized poly(ethylene oxide) (PEO) as a matrix, but the room temperature ionic conductivity was orders of magnitude lower than the conventional lithium battery containing organic solvents. Recently, researchers demonstrated the feasibility of producing solvent-free solid electrolyte by doping with succinonitrile (SCN) plastic crystals for lithium ion transport. They showed that only a small amount of lithium salt (1 mol %) was needed to achieve reasonably high ionic conductivity—on the order of 10−4 S cm−1—despite the fact that SCN itself is a poor ionic conductor. However, the plastic crystal matrix is a waxy substance without sustainable mechanical integrity thereby preventing its full utilization as solid electrolyte.
Others have attempted to create solvent-free polymeric electrolyte membranes by combining PEO with photo-curable poly(ethylene glycol) dimethacrylate (PEGDMA) (to afford mechanical strength) and SCN (for lithium ion transport). Recently, a respectable room temperature ionic conductivity on the order of 10−4 S cm−1 was achieved with the aid of SCN plastic crystal matrix, the conductivity approaching the level of 10−3 S cm−1 at elevated temperatures higher than 80 C. Although promising, this polymeric electrolyte has to rely on the plastic crystal phase of SCN in the PEO/PEGDMA matrix to achieve both sufficiently high ionic conductivity and mechanical strength.
Indeed, in U.S. Published Patent Application No. 2012/0094187, The present invention depart from this current technology by avoiding the formation of a plastic crystal matrix, focusing instead on completely amorphous mixtures of crosslinkable polyether/SCN/lithium salt.